Welding operations often employ the use of inert or semi-inert gases, e.g., helium, argon, carbon dioxide, etc., as a shielding gas to protect the weld area. Air in the weld zone is displaced by a shielding gas in order to prevent contamination of the molten weld puddle. This contamination is caused mainly by nitrogen, oxygen and water vapor present in the atmosphere. As an example, nitrogen in solidified steel reduces the ductility and impact strength of the weld and can cause cracking. In large amounts, nitrogen can also cause weld porosity. Excess oxygen in steel combines with carbon to form carbon monoxide (CO). This gas can be trapped in the metal, causing porosity. In addition, excess oxygen can combine with other elements in steel and form compounds that produce inclusions in the weld metal. When hydrogen, present in water vapor and oil, combines with either iron or aluminum, porosity will result and “underbead” weld metal cracking may occur. Argon, helium and carbon dioxide can be used alone, in combinations or mixed with other gases to provide defect free welds in a variety of weld applications and weld processes.
Metal Inert Gas (“MIG”) welding is negatively impacted by excess shielding gas flow rate, and requires minimizing turbulent gas flow to exclude air from the arc. Several devices are used to set shielding gas flow rates. One is used on the cylinder or pipeline gas supply, e.g., a flowmeter with a flow control knob. The knob adjusts a needle valve that lowers the pressure in the gas delivery hose to that needed to achieve the desired flow of shielding gas, typically employing a float ball. Another is only for cylinder gas supply, and employs a very small orifice and varies the pressure upstream of the orifice using a regulator to control flow.
It is important that the flow rate set on the flowmeter or regulator remain at the set value while welding. However, restrictions occur in production which alter flow such as spatter build-up in the MIG gun nozzle, twists occurring in the gas passages in the MIG gun cable, or debris build-up in the conduit passage sections. In an effort to minimize the above variations, choked flow systems were developed. These systems required higher pressure upstream of the restriction of the orifice or valve. However, high pressure causes an initial gas surge, which is undesirable toward achieving high quality welds. In fact, excessively high gas surges at the start of the welding process allows air to be mixed with the gas stream and can cause internal weld porosity until steady state is achieved.
Low-pressure devices equally suffer from problems. These systems typically lack the automatic flow compensation of high pressure devices, and insufficient extra gas at the start of the welding operation causes inferior weld starts.
Overflow as well as underflow from the gas line to the welding torch causes initial weld irregularities, including spatter, porosity, and contamination of the weld. Therefore, it is desired to reduce and/or minimize the variation of shielding gas flow.
Finally, different brands of welding guns and different locations may have different flow characteristics that may further affect the flow of gas. Pressure or volume-based flow controllers do not have means for determining the flow rate that actually passes to the weld site, and therefore variations in flow from a gas source or through the weld gun will not be captured by the flow controller. Therefore, there is recognized a need for an improved gas flow controller that is capable of regulating the flow of a shielding gas to a welding operation, particularly during start-up.